1. Field of the Invention
The invention relates to microstrip to microstrip transitions and more particularly to a transition designed to traverse a hermetic seal and to be fabricated using printed circuit techniques.
2. Prior Art
Microstrip transmission lines are a common form of transmission line in high frequency circuits. The microstrip transmission line is the transmission line of choice in high frequency circuits requiring active components or the inclusion of monolithically integrated circuits in a hybrid mode of assembly. In such applications the provision of a conductor formed on the upper surface of a ceramic substrate having a ground plane on its under surface, provides an efficient and convenient mode of high frequency transmission and is the conventional choice for active circuits.
Microwave electronics circuits with multiple chips now generally require a hermetic and often an RF shielding enclosure. When such an enclosure is required, efficient means must be provided for coupling RF signals to and from the enclosed electronics circuits.
Since printed circuit techniques are used to pattern the microstrip lines between the circuits within the hermetic enclosure, it is desirable to form the transition using the same processing steps.
The "modules" as these hermetically packaged electronic assemblies are frequently called, typically employ an alumina substrate to which integrated circuits (MMICs at high frequencies) ar bonded and which have microstrip conductors on their upper surfaces and a general ground plane on their under surfaces for point to point high frequency transmission. Below the ground plane a multilayer thick film dielectric is often added to the assembly to supply the energization and provide low frequency control signals. The thick film dielectric usually consists of several dielectric layers each supporting a patterned metallization applied by standard thick film techniques.